Criminals might soon be identified by a single strand of hair – even 250 years later

DNA evidence has shined a light on many a mystery, from helping trace the roots of the Great Plague to adding critical plot twists to every other episode of CSI: Crime Scene Investigation. But DNA samples are easily degraded and when subjected to things like light and heat they can become pretty useless pretty quickly. Scientists have now come up with a method that they are hailing as a game-changer for forensics, using analysis of hair samples to detect unique patterns of proteins that can identify humans up to 250 years after being left behind.

Often described as the building blocks of life, amino acids are organic compounds that can be found in animals, plant tissue and recently, comet atmospheres. When they link together in a chain, they become what we call proteins, which are built in a way that is based on coding instructions from DNA, as this video points out.

What biochemist at Lawrence Livermore National Laboratory (LLNL) Glendon Parker has discovered, is that there are certain kinds of proteins that can be connected back to a person's unique DNA. These are called single amino acid polymorphisms (SAPs) and arise from DNA mutations that result in amino acid substitutions. While the proteins themselves are not inherited, the DNA that produces them is.

"As a result, there is a link between the protein markers that we find and a person's DNA," says Deon Anex, an LLNL chemist and co-author on the study. "There are two reasons why this is particularly important: the DNA is unique to each individual and it is inherited from a person's parents."

The team analyzed hair samples from 66 European-Americans, five African Americans, five Kenyans and six skeletal remains and have found a total of 185 protein markers so far. The amount of markers in the hair, along with their pattern, is unique to the individual, and the researchers say their current sample size would enable them to identify a single person among a population of one million.

And because the hair samples taken from the skeletal remains were between 150 and 250 years old, it demonstrates how much more chemically robust proteins are than nuclear DNA and therefore shows how this technique could address some current roadblocks in forensic science.

"We are in a very similar place with protein-based identification to where DNA profiling was during the early days of its development," says LLNL chemist Brad Hart, co-author of a paper detailing the work. "This method will be a game-changer for forensics, and while we've made a lot of progress toward proving it, there are steps to go before this new technique will be able to reach its full potential."

Currently, the process takes two and a half days, though the team is now working on optimizing the methodology. Ultimately, it aims to refine its work and establish a set of 90 to 100 protein markers that could be used to identify a human among the world's population using a single strand of hair, and believes improvements in sample processing and instrumentation method can take them there.

"The discovery phase has been quite complex, but once the technique is established, we believe it can be made into a routine procedure for use in crime labs," says Anex.

The research was published in the journal PLOS ONE, and you can hear from the scientists in the video below.